Photosynthesis Energy Conversion 4

Question 1

Which thermodynamic principle explains why photosynthesis requires continuous light energy input?

Accepted Answer

The Second Law of Thermodynamics — converting low-entropy light into high-entropy heat is spontaneous, but the reverse requires energy input

Answer

Boyle's Law — gas volume must stay constant

Answer

Conservation of mass — atoms must be recycled continuously

Answer

The First Law — energy cannot be created, only found in sunlight

Question 2

At what point in the electron transport chain of thylakoids is the proton gradient across the membrane established?

Accepted Answer

At the cytochrome b6f complex and during water splitting on the lumenal side

Answer

Only during cyclic electron flow

Answer

Only at PSI when NADP+ is reduced

Answer

Only at ATP synthase when protons flow back

Question 3

Why does isolated spinach chloroplast thylakoid membrane fluoresce red light when illuminated in vitro?

Accepted Answer

Because chlorophyll molecules that cannot transfer energy to a reaction center re-emit photons at longer wavelengths

Answer

Because rubisco emits red light during CO2 fixation

Answer

Because ATP synthase catalyzes a chemiluminescent reaction

Answer

Because carotenoids absorb blue and re-emit red

Question 4

What is the Emerson enhancement effect, and what does it reveal about photosynthesis?

Accepted Answer

Using two light wavelengths simultaneously produces more O2 than either alone predicts, proving two photosystems work cooperatively

Answer

Longer light exposure always doubles photosynthetic output

Answer

Red light alone maximizes photosynthesis in all species

Answer

The Calvin cycle rate doubles at 700 nm illumination

Question 5

In C4 plants, how does spatial separation of reactions improve energy conversion efficiency?

Accepted Answer

CO2 is concentrated around rubisco in bundle-sheath cells, suppressing photorespiration

Answer

Chloroplasts in mesophyll cells produce O2 that is immediately used in bundle-sheath ATP synthesis

Answer

Stroma lamellae are moved to vacuoles to reduce water loss

Answer

G3P is converted to glucose in the epidermis to save energy

Question 6

Which compound directly links the light-dependent reactions to the Calvin cycle by carrying both energy and reducing power?

Accepted Answer

ATP and NADPH together

Answer

Glucose-6-phosphate

Answer

Plastoquinone

Answer

Ferredoxin

Question 7

What is the free energy change (ΔG) for the overall photosynthesis reaction, and what does its sign indicate?

Accepted Answer

ΔG ≈ +2870 kJ/mol; reaction is non-spontaneous and requires energy input

Answer

ΔG ≈ −2870 kJ/mol; reaction is spontaneous

Answer

ΔG = 0; reaction is at equilibrium

Answer

ΔG ≈ −686 kJ/mol; reaction releases heat